Add exec section to provide cmd output to the LLM

[juodumas]

Is there any interest in this feature?

Before the change:

>>> user

what does the `-W` flag for `git diff` do?

<<< assistant

The `-W` flag for `git diff` is used to ignore whitespace changes.<...>

After the change:

>>> exec

man git-diff

>>> user

what does the `-W` flag for `git diff` do?

<<< assistant

The `-W` or `--function-context` flag for `git diff` is used to show the whole function as context lines for each change.<...>

[madox2]

Yes, it looks nice! That would allow us to be even more creative about prompts.